THERMOLUMINESCENCE DOSIMETER READERS

D. C. Rlvero-Ramrrez1, c. Garda-TrapaQa', N. Pavón-Gonzalez1, F.

E. Draz-BernaP & D. Mollna-RodrrQuezJ

Benavldes-Benrtez2,Qulles-La Torre2, J

1 Institute for Technology and Applied Science Nuclear, InSTEC

Ave. Salvador Allende y Luaces, Quinta de los MolinosAP 6163, CP10600 Plaza. Ciudad Habana, Cuba

doris@tctn.isctn.edu.cu

2Cordoba UniversityMenendes Pidal sInCP14009, Cordoba, Spain

JCenter of Protection and Hygiene of the RadiationsLa Quebrada. San José. Habana. Cuba

Received: Oecember 31"', 2003. Accepted March ~, 2003

ABSTRAG

The thermolumlnescence doslmeter (TLD) readers used In the Laboratory of External DoSlmetry of the Center of

Protectlon and HyQlene from the Radlatlons are old-fashloned. The data obtalned by thls equlpment must be

manually wrltten down In arder to subsequently, process them and these data do not remaln reQlstered In any

memory for future analysls. Thls paper describes the deslQn and creatlon of a system that conneds these TLD

readers to a personal computer. The system Includes a data acqulsltlon card wlth several analoQue input channels,

counters, tlmers as well as dlQltallnputS/outputs and software, In arder to control the acqulsltlon and processlnQ of

the data.

RESUMEN

Los lectores de dosímetros termolumlnlscentes (TLD) que se usan en el Laboratorio de Doslmetría Externa del

Centro de Protección e HIQlene de las Radiaciones son antlQuos. Los datos obtenidos con estos equipos deben ser

tomados manualmente para ser procesados y no quedan reQistrados en nlnQuna otra parte para su futuro análisis.

Este trabajo describe el diseño y construcción de un sistema que conecta estos lectores de TLD a una computadora

personal. Este sistema Incluye una tarjeta de adquisición de datos con varios canales de entradas analóQicas,

contadores -temporizadores, así como entradas/salidas dlQltales y además un proQrama encarQado del control de

la adquisición v el Drocesamlento de los datos.

KEYVVORDS: Thermoluminescence, Dosimeter, Data AcQuisltlon, Doslmetrv. Dose Evaluation.

INTRODUGION

Some solld materials have the ablllty of malntalning the energy absorbed when interadlng with ionizlng radlation.

Later, when these substances are heated to a certain temperature, they can emit part of that ener~y converted into

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light. This feature is called thermoluminescence (TL). Thermoluminescence as a dosimetric method Is one of the most

frequently employed in the world today. Thermolumlnescence dosimeters (TLD) are applied in envlronmental

dosimetry, radiotherapy, radiodlagnosls and radiologlcal emergencies partlcularly In personal dosimetry. In our

country, thls method has been employed In radiodiagnosls, industrial applications, education and metrology for

several years.

Three parts or systems constitute the TLD readers. One of them Is a heating system, whlch applies heat to the TL

doslmeter. This system must be capable to guarantee an adequate reproduclbllity of thls process. The next part is a

Ilght detectlng system, whlch has the functloh of detedlng the pulses of the light emltted by the TL dosimeter during

the heatlng process. The last part Is a reglstratlon system, which records signals.

The Center of Protedlon and Hyglene from Radlatlons (CPHR), In Havana, emp.¡oys thls technlque In environmental

radlological vlgllance and personal doslmetry. For this purpose, they have two TLD readers: a VINTEN 654 and a

HARSHAW 2000 B/C. Both TL readers are executlng manually all the measurements and data processlng.

The thermolumlnescence dosimetry offers the possibllity of automatlon of all measurement and informatlon handling

processes. Thls Is especlally Important when personal doslmetry facilities wlth a large number of users are offered.

One can now purchase totally automated readers that Include the acqulsltlon programs, analysls and processing of

the data. These programs can also be offered separately. However, the employment of these programs Is limited to

the equlpments for which those programs were developed. This sltuatlon becomes more complex If they are old

fashioned and delivered by dlfferent manufadures, as in the case of the CPHR equipment.

On the other hand, one of the important topics to keep in mind in personal dosimetry is the speed of acquiring

results of the seNice. Thus, the speed of processlng the informatlon is converted into an important fador within this

task. We have approached thls by conneding the reader to a personal computer iPC) and by developlng a program

for data acqulsltlon and processing. Havlng a program wlth the already mentloned charaderistlcs would also permit to

Increase the speed In the processlng of the final results. At the same time, thls program ensures the quallty of the task

executlon, decreasing the influence of the human fador in the results. These two aspedS are very important when

applyin~ TL doslmetry to radlolo~lcal emer~encles.

One of the disadvantages of thermolumlnescence dosimetry using manual readers, in relation to other doslmetric

methods, is that the Information 15 lost once the reading has been done. This problem can be solved by employing

the previously mentioned programs, which allow us to save the information for further analysis.

The alm of this work is to show the design and assemble of a system to connect two exlstlng TLD readers to a PC. The

system Includes a data acqulsltion card wlth several analogue Input channels, counters, tlmers as well as digltal

Inputs/outputs and software In order to achieve the acqulSltlon and processlng of data.

2. DESCRIPTION OF THE SYSTEM

Ta cammunlcate the TLD readers with a PC, we use a data acquisltian card develaped in the Universlty af Cardaba [1

3]. This card has the fallawing characteristics:

8 analogue inputs with the following parameters: 12 bits of resolution, 500 KS/s, 8 gains, programmable

interval and number of conversion.

Analogue-to-digital conversion bya D/A converter with 12 bjts of resolution buffered and with unipolar (0-5 V)

output.Group of 2x3 16 programmable bits timers.

Group of 3x8 dig.itallnput/Output Ports.

Transference of data from the FIFO by poll.ing, DMA and interruptions.

Complete Interface with the AT BUS.

Selection of the DMA channels and Interruptions by means of jumpers.

Selection of the address range by means of a dlp switch.

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This card can be dlvided into several blocks as shown in Fig.l. These blocks are: the interface with the AT bus, the

control block. the Interruptlon block. the timer block. the digitallnputs and outputs, the analogue-to-digital conversion

block. the dlgltal-to-analogue conversion block. the analogue inputs Interface and the analog outputs interface.

Figure 7. lñe ADQ card block diagram

The Interface wlth the AT BUS Block adapt5 the level5 of the 5ignal5 to the AT BUS 5pecificatlon5 and 15 constituted by

drlver5 and jumper5.

The Control Block carrres out Qeneral control functions. It Qenerates all the slQnals assoclated to the dlfferent ways of

accessinQ the ADQ. The block is composed by two PAL. a maQnltude comparlnQ device, two decoders and a mlcro

switch.

The Interruptlons Block: An interruptlon's controller 82C59 constltutes this block. It provides the control of the 8

demands of interruption that exist in the card. Thls controller allows different possibilitles like masklng, adlvatlon by

flank or leveí and rotatlonal or flxed prlority. The recognitlon of the interruptions by the microprocessor can be done

by POLLING or bythe INTAsignal.

The Analogue-to-Dlgltal Converslon Block allows to achleve the conversion of analogue signals, whlch appear In one

of the eight analogue input channels. We will divide it In several sub-blocks for its detailed description:

Converter and FIFO sub-block. An analogue-to-dlgital converter of 12 bit5, 500 Ks/S frequency of conver51on

and a range of analogue Input5 of :t5 VOlt5 con5t1tute thi5 5ubblock. The FIFO has a 51ze of 512 x12,

extendable to 4Kx12. The re5ult of the conver51on5 15 automatlcally stored in the memory after de conver51on

15 flnl5hed.

77mer sub-block. The timers generate the "start of conversion" signals at the programmed frequency and

count the achieved conversions.

Reglsters sub-b/ock. It 15 con5tituted by four regi5ter5 who5e content5 determine the parameter5 of the

conver5ion, e.g., 5eleded channel5, trlggering, gain, converter condltion, reading mode, etc

Control sub-block. It controls the correct functloning of the analogue-to-digital conversion in every aspect.

The Tlmers block includes six timers made up of two 82C54. They can be programmed to control the operations of the

automatic analogue-to-digital and digital-to-analogue conversion. They can also be avallable for any other

temporization task.

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The Digltal-to-Analogue Converslon Block. Two dlgital-to-ana!ogue converters and an addltiona! circuit that allows

generatlnQ severa! types of output siQnals constitute thls block:

When operating, one of the converter5 15 controlled by the hO5t computer mlcroproce550r. Thl5 mean5 that

the mlcroproce550r can tran5fer the corre5ponding data to the Input latch of the converter at any time. Thl5

output can be unlpolar or blpolar depending on the configuratlon 5eleded by the Jumper .

.The other converter operates automatically. This allows to produce an analogue signal of a specific type and

duratlon, ieven periodical. Therefore, it provides a 4K x12blt RAM. This memory can be written down by the

microprocessor of the host computer with the appropriate value and subsequently be addressed to the latch

of the converter wlth the programmed frequency and periodlcit.y.

The Analogue Input Block is a block for handling analogue input signals. The user can programme this block to get

the conversion as accurate as posslble. This block permits the following tasks:

COnneding with 8 channels, uslng only one converter.

OfferinQ the user 8 QainS for every channel So that he can ChooSe the most suitable one to obtain the best

resolution.

The AnaloQue Outputs Block. Two operational amplifiers constitute thls block. Theseampliflers are In follower

conflQuration to achieve low output Impedance and protect the converters.

The DIQltallnputs/Outputs Block is constituted by the 82C55 and has three ports 8 blts, which are accesslble In the DIN

connector. The use of this circuit provldes us with a Qreat flexibility since It has several proQrammlnQ modes.

HARSHAW

Figure 2. Blocks scheme of the system

In the back panel of every TLD reader, we flnd the signal corresponding to the temperature at which the TL

doslmeters are heated, and the pulses from the photomultiplier tube, correspondlng to the Iight emitted by the TL

dosimeters during the heating process. We conned these signals and the one that marks the beginning of the

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heatlng ofTL doslmeters to the card by means ofan adapter, as Fig.2 shows [4]. Thls adapter only has the function of

coupllng levels of signs and types of connectors.

The temperature slgnal is connected to the analogue input, the pulses are conneded to the counter Input and the

signal that indicates the start of the heating process Is conneded to the.dlgitallnput of the ADQ card. In thls way the

system can be programmed to build a thermoluminescence curve (Glow Curve) and to calculate the doses whenever

a doslmetric pIllIS read.

3. DESCRIPTION OF THE SOFlWARE

The created system also Includes an appllcatlon and control software. Thls software controls the card, gets the

acqulred data from the readers, dlsplays the thermolumlnescence curve and calculates the doses.

Thls program was wrltten in Visual Basic language. There 15 a menu at the top ofthe maln window (FIg 3). Same ofthe

optlons are In a tool bar, below the menus. These tools speed up the access to several optlons In the software [4].

FigureJ. Principal windows with lñermoluminescence Curve

Some of the most Imoortant oDtlons In the menu are:

Acqulsltlon: In thls option the user can acqulre and display the curves of thermolumlnescence associated to an

examlned TLD (Flg.3 ). It allows to get the hlghest value of the temperature In each step of the heatlng cycle as well as

calculatlng the integral of the reglon of Interest of the curve. The curves and the associated parameters can be saved

for their future analysis.

Befare QettlnQ inta the acquisitlan, the data flles can be classifjed accardinQ the klnd af daslmeters usaQe: in

backQraund, In calibratlan ar In arder ta evaluate. AccardinQ ta thls classlfjcatlan, the praQram will request speclfjcdata, e.Q., far daslmeters calibratlan, it wlll ask the dase ta which they are irradlated, ar camman data ta all

acqulSltlan, Ilke number af dasimeters, number af measurements far daslmeters, label af dasimeters Qraup, etc.

(Fi~.4).

Figure 4. Demanded data for dosimeters to eva/uate

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The Integral of the seleded area In the thermoluminescence curve, date and code of the dosimeter are saved in a

database for their future processing. The program also enables the identiflcation of the doslmetersby means of Its bar

code.

Quallty Control: In this option, the system achleves the operatlons qssodated wlth the quality parameters of the

reader VINTEN 654. These include the acqulsition of the siQnals arrivlnQ from: the internalliQht source (ILS) (FIQ 5), the

externalliQht source (ELS), the siQnals produced in the dark current (DC) and the slQnals derived from the readlng

wlthout detedor. It achleves the processinQ and visualizatlon of that informatlon in time.

Figure 5. Input parameters for the measurement ofthe interna/ /ight source

Evaluatlon: In thls option the user calculates the dose ofone or several doslmeters, having the Integral of the seleCted

area of Its curve. To do thls, he must choose one or several calibration files, as well as one or several background flles

(Flg 6). The chosen files are taken from the system database, whlch distinguishes them by Its date of acquisition or by

a label that can be given to each file.

Figure 6. Dose ca/cu/ation windows

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Imlrnrll nf Ann/1pd Ilp~parrh and TechnoloOv

The results of the dose calculatlon are organized according to the entity and the period In which the data were taken

By entlty we mean the projects, the institutlons, etc.

The values of dose are shown on the screen and can be prlnted in a definite format for thelr subsequent analysls.However, thls is useful only when the program 15 used In the _dose evaluation of several applicationS of

thermolumlnescence doslmetry apart from personal doslmetry. In thls case the system has a database with the cllents'

entlty, as well as the perlods and codes of the dosimeters, to facilltate the use of the program. The results of the dose

evaluatlon are sent diredly to the database to be saved, and to have a control of the doses recelved by the

occupatlonal exposed workers clients of the personal doslmetry facility [5].

4. CONClUSIONS

As a result of thls work we have developed a system for the acqulsltlon and processlng of data generated by manual

TLD readers. The system allows the storage of the acqulred data in a computer; the processlng and control of the data

obtalned from the test and the control ofthe reader. Finally, it also perm.its the evaluatlon ofthe do~e.

The program also facilitates the transference of the evaluated doses to the database In order to admlnister personal

dosimetrv results.

The use of thls system has facilitated the operatlon of manual TLD readers In routlne control wlth a considerable

amount of work. achlevlng an increase of speed In the process. Furthermore, Its usage has dlmlnlshed the influence

of the human fador In the final result.

5. REFERENCES

[1]

[2]

[3]

[4]

Quiles F .J" Benavides, J, I. Salcines E. G., Perez R, G. Implementación de Instrumentos Vlrtuales para PC,

Compatibles. INFORMATICA 96, Proceedlngs in magnetlc support (dlskette ). Havana. Cuba, 1996.

Rlvero D, Qulles F. J., Benavides J.I, Uso de la tarjeta ADQ para automatizar experimentos. 1 er NURT. 1997.

Havana. Cuba, 1997.Quiles F.J" BenavidesJ.I" Ortlz M. A., Sáez E. y Rlvero D. Mundo Eledrónico, 285, pp, 62-64, 1998.Díaz E" Molina D., Rlvero D., García c. Sistema para el Procesamiento de los datos de Lectores de Dosímetros

Termoluminlscentes, V Regional Congress of Radiologlcal Protedlon, 2001, Recife, Brazll. Proceedlngs in CD,

2001.Manzano de Armas et al, Sistema de gestión de datos en dosimetría personal 'Dosis', V Regional Congress of

Radlologlcal Protectlon, 2001, Recife, Brazil. Proceedings in CD, 2001,[5]

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